Method for transmitting/receiving synchronization signal for d2d communication in wireless communication system, and apparatus therefor

ABSTRACT

The present invention relates to a method and an apparatus which enable a terminal to transmit a signal for device-to-device (D2D) communication in a wireless communication system. Specifically, the present invention transmits a synchronization signal for D2D communication and a demodulation reference signal (DM-RS) for demodulation of the synchronization signal, wherein the base sequence of the demodulation reference signal is generated using a synchronization reference ID.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method of transmitting and receiving asynchronization signal for device-to-device (D2D) communication in awireless communication system and an apparatus therefor.

BACKGROUND ART

A 3rd generation partnership project long term evolution (3GPP LTE)(hereinafter, referred to as ‘LTE’) communication system which is anexample of a wireless communication system to which the presentinvention can be applied will be described in brief.

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS) which is an exampleof a wireless communication system. The E-UMTS is an evolved version ofthe conventional UMTS, and its basic standardization is in progressunder the 3rd Generation Partnership Project (3GPP). The E-UMTS may bereferred to as a Long Term Evolution (LTE) system. Details of thetechnical specifications of the UMTS and E-UMTS may be understood withreference to Release 7 and Release 8 of “3rd Generation PartnershipProject; Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), basestations (eNode B; eNB), and an Access Gateway (AG) which is located atan end of a network (E-UTRAN) and connected to an external network. Thebase stations may simultaneously transmit multiple data streams for abroadcast service, a multicast service and/or a unicast service.

One or more cells exist for one base station. One cell is set to one ofbandwidths of 1.44, 3, 5, 10, 15 and 20 MHz to provide a downlink oruplink transport service to several user equipments. Different cells maybe set to provide different bandwidths. Also, one base station controlsdata transmission and reception for a plurality of user equipments. Thebase station transmits downlink (DL) scheduling information of downlinkdata to the corresponding user equipment to notify the correspondinguser equipment of time and frequency domains to which data will betransmitted and information related to encoding, data size, and hybridautomatic repeat and request (HARQ). Also, the base station transmitsuplink (UL) scheduling information of uplink data to the correspondinguser equipment to notify the corresponding user equipment of time andfrequency domains that can be used by the corresponding user equipment,and information related to encoding, data size, and HARQ. An interfacefor transmitting user traffic or control traffic may be used between thebase stations. A Core Network (CN) may include the AG and a network nodeor the like for user registration of the user equipment. The AG managesmobility of the user equipment on a Tracking Area (TA) basis, whereinone TA includes a plurality of cells.

Although the wireless communication technology developed based on WCDMAhas been evolved into LTE, request and expectation of users andproviders have continued to increase. Also, since another wirelessaccess technology is being continuously developed, new evolution of thewireless communication technology will be required for competitivenessin the future. In this respect, reduction of cost per bit, increase ofavailable service, use of adaptable frequency band, simple structure andopen type interface, proper power consumption of the user equipment,etc. are required.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method oftransmitting and receiving a synchronization signal for D2Dcommunication in a wireless communication system and an apparatustherefor.

The technical objects that can be achieved through the present inventionare not limited to what has been particularly described hereinabove andother technical objects not described herein will be more clearlyunderstood by persons skilled in the art from the following detaileddescription.

Technical Solution

According to an aspect of the present invention devised to solve theabove problems, a method of transmitting a signal for device-to-device(D2D) communication by a user equipment (UE) in a wireless communicationsystem includes transmitting a synchronization signal for D2Dcommunication and a demodulation reference signal (DM-RS) fordemodulating the synchronization signal, wherein a base sequence of theDM-RS is generated using a synchronization reference identity (ID).

The base sequence may be generated based on a value obtained by dividingthe synchronization reference ID by a predetermined value.

An orthogonal cover code (OCC) for the DM-RS may be determined using onelower bit of the synchronization reference ID.

A cyclic shift for the DM-RS may be determined using three lower bits ofthe synchronization reference ID.

According to another aspect of the present invention, a user equipment(UE) for transmitting a signal for device-to-device (D2D) communicationin a wireless communication system includes a radio frequency (RF) unitand a processor, wherein the processor is configured to transmit asynchronization signal for D2D communication and a demodulationreference signal (DM-RS) for demodulating the synchronization signal,and wherein a base sequence of the DM-RS is generated using asynchronization reference identity (ID).

Advantageous Effects

According to the present invention, synchronization signal transmissionand reception can be efficiently performed in a wireless communicationsystem.

Effects according to the present invention are not limited to what hasbeen particularly described hereinabove and other advantages notdescribed herein will be more clearly understood by persons skilled inthe art from the following detailed description of the presentinvention. That is, unintended effects of the present invention may alsobe derived by those skilled in the art from the embodiments of thepresent invention.

DESCRIPTION OF DRAWING

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS) which is an exampleof a wireless communication system.

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a user equipment andE-UTRAN based on the 3GPP radio access network standard.

FIG. 3 is a diagram illustrating physical channels used in a 3GPP LTEsystem and a general method for transmitting a signal using the physicalchannels.

FIG. 4 is a diagram illustrating a structure of a radio frame used in anLTE system.

FIG. 5 is a diagram illustrating a primary broadcast channel (P-BCH) anda synchronization channel (SCH).

FIG. 6 illustrates a radio frame structure for transmission of asynchronization signal (SS).

FIG. 7 illustrates a secondary synchronization signal (SSS) generationscheme.

FIG. 8 illustrates a resource grid of a DL slot.

FIG. 9 illustrates the structure of a DL subframe.

FIG. 10 illustrates the structure of a UL subframe in an LTE system.

FIG. 11 is a diagram for conceptually explaining D2D communication.

FIG. 12 is a diagram referenced to illustrate basic transmission timingsof a D2DSS and a PD2DSCH.

FIG. 13 is a diagram referenced to illustrate the main period and subperiod of a PD2DSCH.

FIG. 14 is a diagram referenced to explain a method of indicating aframe number varying with whether an RV is present according to thepresent invention.

FIG. 15 is a diagram referenced to explain omission of PD2DSCHtransmission in part of a sub period according to the present invention.

FIG. 16 illustrates control information piggybacking according to thepresent invention.

FIG. 17 is a diagram referenced to explain a PD2DSCH change notificationusing a paging signal.

FIG. 18 and FIG. 19 are diagrams referenced to explain the basestructure of an SS associated with D2D communication to which thepresent invention is applied.

FIG. 20 is a diagram referenced to explain the case in which a CRC maskis used as a PD2DSCH format indicator according to the presentinvention.

FIG. 21 is a diagram referenced to explain the case in which an index ofa synchronization resource is indicated through a CRC mask according tothe present invention.

FIG. 22 illustrates a BS and a UE that are applicable to an embodimentof the present invention.

BEST MODE

The following technology may be used for various wireless accesstechnologies such as CDMA (code division multiple access), FDMA(frequency division multiple access), TDMA (time division multipleaccess), OFDMA (orthogonal frequency division multiple access), andSC-FDMA (single carrier frequency division multiple access). The CDMAmay be implemented by the radio technology such as UTRA (universalterrestrial radio access) or CDMA2000. The TDMA may be implemented bythe radio technology such as global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by the radio technologysuch as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, andevolved UTRA (E-UTRA). The UTRA is a part of a universal mobiletelecommunications system (UMTS). A 3rd generation partnership projectlong term evolution (3GPP LTE) is a part of an evolved UMTS (E-UMTS)that uses E-UTRA, and adopts OFDMA in a downlink and SC-FDMA in anuplink. LTE-advanced (LTE-A) is an evolved version of the 3GPP LTE.

For clarification of the description, although the following embodimentswill be described based on the 3GPP LTE/LTE-A, it is to be understoodthat the technical spirits of the present invention are not limited tothe 3GPP LTE/LTE-A. Also, specific terminologies hereinafter used in theembodiments of the present invention are provided to assistunderstanding of the present invention, and various modifications may bemade in the specific terminologies within the range that they do notdepart from technical spirits of the present invention.

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a user equipment andE-UTRAN based on the 3GPP radio access network standard. The controlplane means a passageway where control messages are transmitted, whereinthe control messages are used by the user equipment and the network tomanage call. The user plane means a passageway where data generated inan application layer, for example, voice data or Internet packet dataare transmitted.

A physical layer as the first layer provides an information transferservice to an upper layer using a physical channel. The physical layeris connected to a medium access control (MAC) layer via a transportchannel, wherein the medium access control layer is located above thephysical layer. Data are transferred between the medium access controllayer and the physical layer via the transport channel. Data aretransferred between one physical layer of a transmitting side and theother physical layer of a receiving side via the physical channel. Thephysical channel uses time and frequency as radio resources. In moredetail, the physical channel is modulated in accordance with anorthogonal frequency division multiple access (OFDMA) scheme in adownlink, and is modulated in accordance with a single carrier frequencydivision multiple access (SC-FDMA) scheme in an uplink.

A medium access control (MAC) layer of the second layer provides aservice to a radio link control (RLC) layer above the MAC layer via alogical channel. The RLC layer of the second layer supports reliabledata transmission. The RLC layer may be implemented as a functionalblock inside the MAC layer. In order to effectively transmit data usingIP packets such as IPv4 or IPv6 within a radio interface having a narrowbandwidth, a packet data convergence protocol (PDCP) layer of the secondlayer performs header compression to reduce the size of unnecessarycontrol information.

A radio resource control (RRC) layer located on the lowest part of thethird layer is defined in the control plane only. The RRC layer isassociated with configuration, reconfiguration and release of radiobearers (‘RBs’) to be in charge of controlling the logical, transportand physical channels. In this case, the RB means a service provided bythe second layer for the data transfer between the user equipment andthe network. To this end, the RRC layers of the user equipment and thenetwork exchange RRC message with each other. If the RRC layer of theuser equipment is RRC connected with the RRC layer of the network, theuser equipment is in an RRC connected mode. If not so, the userequipment is in an RRC idle mode. A non-access stratum (NAS) layerlocated above the RRC layer performs functions such as sessionmanagement and mobility management.

One cell constituting a base station eNB is set to one of bandwidths of1.4, 3.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to several user equipments. At this time, differentcells may be set to provide different bandwidths.

As downlink transport channels carrying data from the network to theuser equipment, there are provided a broadcast channel (BCH) carryingsystem information, a paging channel (PCH) carrying paging message, anda downlink shared channel (SCH) carrying user traffic or controlmessages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted via the downlink SCH or anadditional downlink multicast channel (MCH). Meanwhile, as uplinktransport channels carrying data from the user equipment to the network,there are provided a random access channel (RACH) carrying an initialcontrol message and an uplink shared channel (UL-SCH) carrying usertraffic or control message. As logical channels located above thetransport channels and mapped with the transport channels, there areprovided a broadcast control channel (BCCH), a paging control channel(PCCH), a common control channel (CCCH), a multicast control channel(MCCH), and a multicast traffic channel (MTCH).

FIG. 3 is a diagram illustrating physical channels used in a 3GPP LTEsystem and a general method for transmitting a signal using the physicalchannels.

The user equipment performs initial cell search such as synchronizingwith the base station when it newly enters a cell or the power is turnedon at step S301. To this end, the user equipment synchronizes with thebase station by receiving a primary synchronization channel (P-SCH) anda secondary synchronization channel (S-SCH) from the base station, andacquires information such as cell ID, etc. Afterwards, the userequipment may acquire broadcast information within the cell by receivinga physical broadcast channel (PBCH) from the base station. Meanwhile,the user equipment may identify a downlink channel status by receiving adownlink reference signal (DL RS) at the initial cell search step.

The user equipment which has finished the initial cell search mayacquire more detailed system information by receiving a physicaldownlink shared channel (PDSCH) in accordance with a physical downlinkcontrol channel (PDCCH) and information carried in the PDCCH at stepS302.

Afterwards, the user equipment may perform a random access procedure(RACH) such as steps S303 to S306 to complete access to the basestation. To this end, the user equipment may transmit a preamble througha physical random access channel (PRACH) (S303), and may receive aresponse message to the preamble through the PDCCH and the PDSCHcorresponding to the PDCCH (S304). In case of a contention based RACH,the user equipment may perform a contention resolution procedure such astransmission (S305) of additional physical random access channel andreception (S306) of the physical downlink control channel and thephysical downlink shared channel corresponding to the physical downlinkcontrol channel.

The user equipment which has performed the aforementioned steps mayreceive the physical downlink control channel (PDCCH)/physical downlinkshared channel (PDSCH) (S307) and transmit a physical uplink sharedchannel (PUSCH) and a physical uplink control channel (PUCCH) (S308), asa general procedure of transmitting uplink/downlink signals. Controlinformation transmitted from the user equipment to the base station willbe referred to as uplink control information (UCI). The UCI includesHARQ ACK/NACK (Hybrid Automatic Repeat and reQuestAcknowledgement/Negative-ACK), SR (Scheduling Request), CSI (ChannelState Information), etc. In this specification, the HARQ ACK/NACK willbe referred to as HARQ-ACK or ACK/NACK (A/N). The HARQ-ACK includes atleast one of positive ACK (simply, referred to as ACK), negative ACK(NACK), DTX and NACK/DTX. The CSI includes CQI (Channel QualityIndicator), PMI (Precoding Matrix Indicator), RI (Rank Indication), etc.Although the UCI is generally transmitted through the PUCCH, it may betransmitted through the PUSCH if control information and traffic datashould be transmitted at the same time. Also, the user equipment maynon-periodically transmit the UCI through the PUSCH in accordance withrequest/command of the network.

FIG. 4 is a diagram illustrating a structure of a radio frame used in anLTE system.

Referring to FIG. 4, in a cellular OFDM radio packet communicationsystem, uplink/downlink data packet transmission is performed in a unitof subframe, wherein one subframe is defined by a given time intervalthat includes a plurality of OFDM symbols. The 3GPP LTE standardsupports a type 1 radio frame structure applicable to frequency divisionduplex (FDD) and a type 2 radio frame structure applicable to timedivision duplex (TDD).

FIG. 4(a) is a diagram illustrating a structure of a type 1 radio frame.The downlink radio frame includes 10 subframes, each of which includestwo slots in a time domain. A time required to transmit one subframewill be referred to as a transmission time interval (TTI). For example,one subframe may have a length of 1 ms, and one slot may have a lengthof 0.5 ms. One slot includes a plurality of OFDM symbols in a timedomain and a plurality of resource blocks (RB) in a frequency domain.Since the 3GPP LTE system uses OFDM in a downlink, OFDM symbolsrepresent one symbol interval. The OFDM symbol may be referred to asSC-FDMA symbol or symbol interval. The resource block (RB) as a resourceallocation unit may include a plurality of continuous subcarriers in oneslot.

The number of OFDM symbols included in one slot may be varied dependingon configuration of a cyclic prefix (CP). Examples of the CP include anextended CP and a normal CP. For example, if the OFDM symbols areconfigured by the normal CP, the number of OFDM symbols included in oneslot may be 7. If the OFDM symbols are configured by the extended CP,since the length of one OFDM symbol is increased, the number of OFDMsymbols included in one slot is smaller than that of OFDM symbols incase of the normal CP. For example, in case of the extended CP, thenumber of OFDM symbols included in one slot may be 6. If a channel stateis unstable like the case where the user equipment moves at high speed,the extended CP may be used to reduce inter-symbol interference.

If the normal CP is used, since one slot includes seven OFDM symbols,one subframe includes 14 OFDM symbols. At this time, first maximum threeOFDM symbols of each subframe may be allocated to a physical downlinkcontrol channel (PDCCH), and the other OFDM symbols may be allocated toa physical downlink shared channel (PDSCH).

FIG. 4(b) is a diagram illustrating a structure of a type 2 radio frame.The type 2 radio frame includes two half frames, each of which includesfour general subframes, which include two slots, and a special subframewhich includes a downlink pilot time slot (DwPTS), a guard period (GP),and an uplink pilot time slot (UpPTS).

In the special subframe, the DwPTS is used for initial cell search,synchronization or channel estimation at the user equipment. The UpPTSis used for channel estimation at the base station and uplinktransmission synchronization of the user equipment. In other words, theDwPTS is used for downlink transmission, whereas the UpPTS is used foruplink transmission. Especially, the UpPTS is used for PRACH preamble orSRS transmission. Also, the guard period is to remove interferenceoccurring in the uplink due to multipath delay of downlink signalsbetween the uplink and the downlink.

Configuration of the special subframe is defined in the current 3GPPstandard document as illustrated in Table 1 below. Table 1 illustratesthe DwPTS and the UpPTS in case of T_(s)=1/(15000×2048), and the otherregion is configured for the guard period.

TABLE 1 Normal cyclic prefix in downlink UpPTS Extended cyclic prefix indownlink Normal Extended UpPTS Special subframe cyclic prefix cyclicprefix Normal cyclic Extended cyclic configuration DwPTS in uplink inuplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s) 2192 ·T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120· T_(s) 20480 · T_(s) 4384 · T_(s) 5120 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

In the meantime, the structure of the type 2 radio frame, that is,uplink/downlink configuration (UL/DL configuration) in the TDD system isas illustrated in Table 2 below.

TABLE 2 Downlink- to-Uplink Uplink- Switch- downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

In the above Table 2, D means the downlink subframe, U means the uplinksubframe, and S means the special subframe. Also, Table 2 alsoillustrates a downlink-uplink switching period in the uplink/downlinksubframe configuration of each system.

The structure of the aforementioned radio frame is only exemplary, andvarious modifications may be made in the number of subframes included inthe radio frame, the number of slots included in the subframe, or thenumber of symbols included in the slot.

FIG. 5 is a diagram illustrating a primary broadcast channel (P-BCH) anda synchronization channel (SCH). The SCH includes a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH). The P-SCH carries a primary synchronization signal (PSS) andthe S-SCH carries a secondary synchronization signal (SSS).

Referring to FIG. 5, in the frame structure type-1 (that is, FDD), theP-SCH is located at the last OFDM symbol of each of slot #0 (i.e., thefirst slot of subframe #0) and slot #10 (that is, the first slot ofsubframe #5) in every radio frame. The S-SCH is located at a previousOFDM symbol of the last OFDM symbol of each of slot #0 and slot #10 inevery radio frame. The S-SCH and the P-SCH are located at neighboringOFDM symbols. In the frame structure type-2 (i.e., TDD), the P-SCH istransmitted through the third OFDM symbol of each of subframes #1 and #6and the S-SCH is located at the last OFDM symbol of slot #1 (i.e., thesecond slot of subframe #0) and slot #11 (i.e., the second slot ofsubframe #5). The P-BCH is transmitted per four radio frames regardlessof the frame structure type, and is transmitted using the first tofourth OFDM symbols of the second slot of subframe #0.

The P-SCH is transmitted using 72 subcarriers (10 subcarriers arereserved and 62 subcarriers are used for PSS transmission) based on a DC(direct current) subcarrier within corresponding OFDM symbols. The S-SCHis transmitted using 72 subcarriers (10 subcarriers are reserved and 62subcarriers are used for SSS transmission) based on the DC subcarrierwithin corresponding OFDM symbols. The P-BCH is mapped into four OFDMsymbols and 72 subcarriers based on a DC subcarrier within one subframe.

FIG. 6 illustrates a radio frame structure for transmission of asynchronization signal (SS). Specifically, FIG. 6 illustrates a radioframe structure for transmission of an SS and a PBCH in frequencydivision duplex (FDD), wherein FIG. 6(a) illustrates transmissionlocations of an SS and a PBCH in a radio frame configured as a normalcyclic prefix (CP) and FIG. 6(b) illustrates transmission locations ofan SS and a PBCH in a radio frame configured as an extended CP.

If a UE is powered on or newly enters a cell, the UE performs an initialcell search procedure of acquiring time and frequency synchronizationwith the cell and detecting a physical cell identity of the cell. Tothis end, the UE may establish synchronization with the eNB by receivingsynchronization signals, e.g. a primary synchronization signal (PSS) anda secondary synchronization signal (SSS), from the eNB and obtaininformation such as a cell identity (ID).

An SS will be described in more detail with reference to FIG. 6. An SSis categorized into a PSS and an SSS. The PSS is used to acquiretime-domain synchronization of OFDM symbol synchronization, slotsynchronization, etc. and/or frequency-domain synchronization and theSSS is used to acquire frame synchronization, a cell group ID, and/or CPconfiguration of a cell (i.e. information as to whether a normal CP isused or an extended CP is used). Referring to FIG. 6, each of a PSS andan SSS is transmitted on two OFDM symbols of every radio frame. Morespecifically, SSs are transmitted in the first slot of subframe 0 andthe first slot of subframe 5, in consideration of a global system formobile communication (GSM) frame length of 4.6 ms for facilitation ofinter-radio access technology (inter-RAT) measurement. Especially, a PSSis transmitted on the last OFDM symbol of the first slot of subframe 0and on the last OFDM symbol of the first slot of subframe 5 and an SSSis transmitted on the second to last OFDM symbol of the first slot ofsubframe 0 and on the second to last OFDM symbol of the first slot ofsubframe 5. A boundary of a corresponding radio frame may be detectedthrough the SSS. The PSS is transmitted on the last OFDM symbol of acorresponding slot and the SSS is transmitted on an OFDM symbolimmediately before an OFDM symbol on which the PSS is transmitted. Atransmit diversity scheme of an SS uses only a single antenna port andstandards therefor are not separately defined. That is, a single antennaport transmission scheme or a transmission scheme transparent to a UE(e.g. precoding vector switching (PVS), time switched transmit diversity(TSTD), or cyclic delay diversity (CDD)) may be used for transmitdiversity of an SS.

An SS may represent a total of 504 unique physical layer cell IDs by acombination of 3 PSSs and 168 SSSs. In other words, the physical layercell IDs are divided into 168 physical layer cell ID groups eachincluding three unique IDs so that each physical layer cell ID is a partof only one physical layer cell ID group. Accordingly, a physical layercell ID N^(cell) _(ID) (=3N⁽¹⁾+N⁽²⁾ _(ID)) is uniquely defined as numberN⁽¹⁾ _(ID) in the range of 0 to 167 indicating a physical layer cell IDgroup and number N⁽²⁾ _(ID) from 0 to 2 indicating the physical layer IDin the physical layer cell ID group. A UE may be aware of one of threeunique physical layer IDs by detecting the PSS and may be aware of oneof 168 physical layer cell IDs associated with the physical layer ID bydetecting the SSS. A length-63 Zadoff-Chu (ZC) sequence is defined inthe frequency domain and is used as the PSS. As an example, the ZCsequence may be defined by the following equation.

$\begin{matrix}{{d_{u}(n)} = ^{{- j}\frac{\pi \; {{un}{({n + 1})}}}{N_{ZC}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where N_(ZC)=63 and a sequence element corresponding to a DC subcarrier,n=31, is punctured.

The PSS is mapped to 6 RBs (=72 subcarriers) near a center frequency.Among the 72 subcarriers, 9 remaining subcarriers always carry a valueof 0 and serve as elements facilitating filter design for performingsynchronization. To define a total of three PSSs, u=24, 29, and 34 areused in Equation 1. Since u=24 and u=34 have a conjugate symmetryrelation, two correlations may be simultaneously performed. Here,conjugate symmetry indicates the relationship of the following Equation.

d _(u)(n)=(−1)^(n)(d _(N) _(ZC) _(-u)(n))*, when N _(ZC) is even number

d _(u)(n)=(D _(N) _(ZC) _(-n)(n))*, when N _(ZC) is oddnumber  [Equation 2]

A one-shot correlator for u=29 and u=34 may be implemented using thecharacteristics of conjugate symmetry. Computational load may be reducedby about 33.3% as compared with the case without conjugate symmetry.

In more detail, a sequence d(n) used for a PSS is generated from afrequency-domain ZC sequence as follows.

$\begin{matrix}{{d_{u}(n)} = \left\{ \begin{matrix}^{{- j}\frac{\pi \; {{un}{({n + 1})}}}{63}} & {{n = 0},1,\ldots \mspace{14mu},30} \\^{{- j}\frac{\pi \; {u{({n + 1})}}{({n + 2})}}{63}} & {{n = 31},32,\ldots \mspace{14mu},61}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Where a ZC root sequence index u is given by the following table.

TABLE 3 N⁽²⁾ _(ID) Root index u 0 25 1 29 2 34

Referring to FIG. 6, upon detecting a PSS, a UE may discern that acorresponding subframe is one of subframe 0 and subframe 5 because thePSS is transmitted every 5 ms but the UE cannot discern whether thesubframe is subframe 0 or subframe 5. Accordingly, the UE cannotrecognize the boundary of a radio frame only by the PSS. That is, framesynchronization cannot be acquired only by the PSS. The UE detects theboundary of a radio frame by detecting an SSS which is transmitted twicein one radio frame with different sequences.

FIG. 7 illustrates an SSS generation scheme. Specifically, FIG. 7illustrates a relationship of mapping of two sequences in the logicaldomain to sequences in the physical domain.

A sequence used for the SSS is an interleaved concatenation of twolength-31 m-sequences and the concatenated sequence is scrambled by ascrambling sequence given by a PSS. Here, an m-sequence is a type of apseudo noise (PN) sequence.

Referring to FIG. 7, if two m-sequences used to generate an SSS code areS1 and S2, then S1 and S2 are obtained by scrambling two differentPSS-based sequences to the SSS. In this case, S1 and S2 are scrambled bydifferent sequences. A PSS-based scrambling code may be obtained bycyclically shifting an m-sequence generated from a polynomial of x⁵+x³+1and 6 sequences are generated by cyclic shift of the m-sequenceaccording to an index of a PSS. Next, S2 is scrambled by an S1-basedscrambling code. The S1-based scrambling code may be obtained bycyclically shifting an m-sequence generated from a polynomial ofx⁵+x⁴+x²+x¹+1 and 8 sequences are generated by cyclic shift of them-sequence according to an index of S1. The SSS code is swapped every 5ms, whereas the PSS-based scrambling code is not swapped. For example,assuming that an SSS of subframe 0 carries a cell group ID by acombination of (S1, S2), an SSS of subframe 5 carries a sequence swappedas (S2, S1). Hence, a boundary of a radio frame of 10 ms may bediscerned. In this case, the used SSS code is generated from apolynomial of x⁵+x²+1 and a total of 31 codes may be generated bydifferent cyclic shifts of an m-sequence of length-31.

A combination of two length-31 m-sequences for defining the SSS isdifferent in subframe 0 and subframe 5 and a total of 168 cell group IDsare expressed by a combination of the two length-31 m-sequences. Them-sequences used as sequences of the SSS have a robust property in afrequency selective environment. In addition, since the m-sequences maybe transformed by high-speed m-sequence transform using fast Hadamardtransform, if the m-sequences are used as the SSS, computational loadnecessary for a UE to interpret the SSS may be reduced. Since the SSS isconfigured by two short codes, computational load of the UE may bereduced.

Generation of the SSS will now be described in more detail. A sequenced(0), . . . , d(61) used for the SSS is an interleaved concatenation oftwo length-31 binary sequences. The concatenated sequence is scrambledby a sequence given by the PSS.

A combination of two length-31 sequences for defining the PSS becomesdifferent in subframe 0 and subframe 5 as follows.

$\begin{matrix}{{d\left( {2n} \right)} = \left\{ \begin{matrix}{{s_{0}^{(m_{0})}(n)}{c_{0}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 0} \\{{s_{1}^{(m_{1})}(n)}{c_{0}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 5}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack \\{{d\left( {{2n} + 1} \right)} = \left\{ \begin{matrix}{{s_{1}^{(m_{1})}(n)}{c_{1}(n)}{z_{1}^{(m_{0})}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 0} \\{{s_{0}^{(m_{0})}(n)}{c_{1}(n)}{z_{1}^{(m_{1})}(n)}} & {{in}\mspace{14mu} {subframe}\mspace{14mu} 5}\end{matrix} \right.} & \;\end{matrix}$

In Equation 4, 0≦n≦30. Indices m₀ and m₁ are derived from aphysical-layer cell-identity group N⁽¹⁾ _(ID) as follows.

$\begin{matrix}{{m_{0} = {m^{\prime}{mod}\; 31}}{m_{1} = {\left( {m_{0} + \left\lfloor {m^{\prime}/31} \right\rfloor + 1} \right){mod}\; 31}}{{m^{\prime} = {N_{ID}^{(1)} + {{q\left( {q + 1} \right)}/2}}},{q = \left\lfloor \frac{N_{ID}^{(1)} + {{q^{\prime}\left( {q^{\prime} + 1} \right)}/2}}{30} \right\rfloor},{q^{\prime} = \left\lfloor {N_{ID}^{(1)}/30} \right\rfloor}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

The output of Equation 5 is listed in Table 4 that follows Equation 11.

Two sequences s^((m0)) ₀(n) and s^((m1)) ₁(n) are defined as twodifferent cyclic shifts of an m-sequence s(n).

s ₀ ^((m) ⁰ ⁾(n)=s((n+m ₀)mod 31)

s ₁ ^((m) ¹ ⁾(n)=s((n+m ₁)mod 31)  [Equation 6]

where s(i)=1−2x(i) (0≦i≦30) is defined by the following equation withinitial conditions x(0)=0, x(1)=0, x(2), x(3)=0, x(4)=1.

x(ī+5)=(x(ī+3)+x( i ))mod 2, 0≦ī≦25  [Equation 7]

Two scrambling sequences c₀(n) and c₁(n) depend on the PSS and aredefined by two different cyclic shifts of an m-sequence c(n).

c ₀(n)=c((n+N _(ID) ⁽²⁾)mod 31)

c ₁(n)=c((n+N _(ID) ⁽²⁾+3)mod 31)  [Equation 8]

where N⁽²⁾ _(ID)ε{0, 1, 2} is a physical-layer identity within aphysical-layer cell identity group N⁽¹⁾ _(ID) and c(i)=1−2x(i) (0≦i≦30)is defined by the following equation with initial conditions x(0)=0,x(1)=0, x(2), x(3)=0, x(4)=1.

x(ī+5)=(x(ī+3)+x( i ))mod 2, 0≦ī≦25  [Equation 9]

Scrambling sequences Z^((m0)1)(n) and Z^((m1)1)(n) are defined by cyclicshift of an m-sequence z(n).

z ₁ ^((m) ⁰ ⁾(n)=z((n+(m ₀ mod 8))mod 31)

z ₁ ^((m) ¹ ⁾(n)=z((n+(m ₁ mod 8))mod 31)  [Equation 10]

where m₀ and m₁ are obtained from Table 4 that follows Equation 11 andz(i)=1−2x(i) (0≦i≦30) is defined by the following equation with initialconditions x(0)=0, x(1)=0, x(2), x(3)=0, x(4)=1.

x(ī+5)=(x(ī+4)+x(ī+2)+x(ī+1)+x( i ))mod 2, 0≦ī≦25  [Equation 11]

TABLE 4 N⁽¹⁾ _(ID) m₀ m₁ 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 88 8 9 9 9 10 10 10 11 11 11 12 12 12 13 13 13 14 14 14 15 15 15 16 16 1617 17 17 18 18 18 19 19 19 20 20 20 21 21 21 22 22 22 23 23 23 24 24 2425 25 25 26 26 26 27 27 27 28 28 28 29 29 29 30 30 0 2 31 1 3 32 2 4 333 5 34 4 6 35 5 7 36 6 8 37 7 9 38 8 10 39 9 11 40 10 12 41 11 13 42 1214 43 13 15 44 14 16 45 15 17 46 16 18 47 17 19 48 18 20 49 19 21 50 2022 51 21 23 52 22 24 53 23 25 54 24 26 55 25 27 56 26 28 57 27 29 58 2830 59 0 3 60 1 4 61 2 5 62 3 6 63 4 7 64 5 8 65 6 9 66 7 10 67 8 11 68 912 69 10 13 70 11 14 71 12 15 72 13 16 73 14 17 74 15 18 75 16 19 76 1720 77 18 21 78 19 22 79 20 23 80 21 24 81 22 25 82 23 26 83 24 27 84 2528 85 26 29 86 27 30 87 0 4 88 1 5 89 2 6 90 3 7 91 4 8 92 5 9 93 6 1094 7 11 95 8 12 96 9 13 97 10 14 98 11 15 99 12 16 100 13 17 101 14 18102 15 19 103 16 20 104 17 21 105 18 22 106 19 23 107 20 24 108 21 25109 22 26 110 23 27 111 24 28 112 25 29 113 26 30 114 0 5 115 1 6 116 27 117 3 8 118 4 9 119 5 10 120 6 11 121 7 12 122 8 13 123 9 14 124 10 15125 11 16 126 12 17 127 13 18 128 14 19 129 15 20 130 16 21 131 17 22132 18 23 133 19 24 134 20 25 135 21 26 136 22 27 137 23 28 138 24 29139 25 30 140 0 6 141 1 7 142 2 8 143 3 9 144 4 10 145 5 11 146 6 12 1477 13 148 8 14 149 9 15 150 10 16 151 11 17 152 12 18 153 13 19 154 14 20155 15 21 156 16 22 157 17 23 158 18 24 159 19 25 160 20 26 161 21 27162 22 28 163 23 29 164 24 30 165 0 7 166 1 8 167 2 9 — — — — — —

A UE, which has demodulated a DL signal by performing a cell searchprocedure using an SSS and determined time and frequency parametersnecessary for transmitting a UL signal at an accurate time, maycommunicate with an eNB only after acquiring system informationnecessary for system configuration of the UE from the eNB.

The system information is configured by a master information block (MIB)and system information blocks (SIBs). Each SIB includes a set offunctionally associated parameters and is categorized into an MIB, SIBType 1 (SIB1), SIB Type 2 (SIB2), and SIB3 to SIB8 according to includedparameters. The MIB includes most frequency transmitted parameters whichare essential for initial access of the UE to a network of the eNB. SIB1includes parameters needed to determine if a specific cell is suitablefor cell selection, as well as information about time-domain schedulingof the other SIBs.

The UE may receive the MIB through a broadcast channel (e.g. a PBCH).The MIB includes DL bandwidth (BW), PHICH configuration, and a systemframe number (SFN). Accordingly, the UE may be explicitly aware ofinformation about the DL BW, SFN, and PHICH configuration by receivingthe PBCH. Meanwhile, information which may be implicitly recognized bythe UE through reception of the PBCH is the number of transmit antennaports of the eNB. Information about the number of transmit antennas ofthe eNB is implicitly signaled by masking (e.g. XOR operation) asequence corresponding to the number of transmit antennas to a 16-bitcyclic redundancy check (CRC) used for error detection of the PBCH.

The PBCH is mapped to four subframes during 40 ms. The time of 40 ms isblind-detected and explicit signaling about 40 ms is not separatelypresent. In the time domain, the PBCH is transmitted on OFDM symbols 0to 3 of slot 1 in subframe 0 (the second slot of subframe 0) of a radioframe.

In the frequency domain, a PSS/SSS and a PBCH are transmitted only in atotal of 6 RBs, i.e. a total of 72 subcarriers, irrespective of actualsystem BW, wherein 3 RBs are on the left and the other 3 RBs are on theright centering on a DC subcarrier on corresponding OFDM symbols.Therefore, the UE is configured to detect or decode the SS and the PBCHirrespective of DL BW configured for the UE.

After initial cell search, a UE which has accessed a network of an eNBmay acquire more detailed system information by receiving a PDCCH and aPDSCH according to information carried on the PDCCH. The UE which hasperformed the above-described procedure may perform reception of aPDCCH/PDSCH and transmission of a PUSCH/PUCCH as a normal UL/DL signaltransmission procedure.

FIG. 8 illustrates a resource grid of a DL slot.

Referring to FIG. 8, a DL slot includes N_(symb) ^(DL) OFDM symbols inthe time domain and N_(RB) ^(DL) in the frequency domain. Each RBincludes N_(sc) ^(RB) subcarriers and thus the DL slot includes N_(RB)^(DL)×N_(sc) ^(RB) subcarriers in the frequency domain. Although FIG. 8illustrates the case in which a DL slot includes 7 OFDM symbols and anRB includes 12 subcarriers, the present invention is not limitedthereto. For example, the number of OFDM symbols included in the DL slotmay differ according to CP length.

Each element on the resource grid is referred to as a resource element(RE). One RE is indicated by one OFDM symbol index and one subcarrierindex. One RB includes N_(symb) ^(DL)×N_(sc) ^(RB) REs. The number ofRBs, N_(RB) ^(DL), included in a DL slot depends on DL bandwidthconfigured in a cell.

FIG. 9 illustrates the structure of a DL subframe.

Referring to FIG. 9, up to three (or four) OFDM symbols at the start ofthe first slot of a DL subframe are used as a control region to whichcontrol channels are allocated and the other OFDM symbols of the DLsubframe are used as a data region to which a PDSCH is allocated. DLcontrol channels defined for the LTE system include a physical controlformat indicator channel (PCFICH), a physical downlink control channel(PDCCH), and a physical hybrid ARQ indicator channel (PHICH). The PCFICHis transmitted in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe. The PHICH delivers a HARQ ACK/NACKsignal as a response to UL transmission.

Control information carried on the PDCCH is called downlink controlinformation (DCI). The DCI transports resource allocation informationand other control information for a UE or a UE group. For example, theDCI includes DL/UL scheduling information, UL transmit (Tx) powercontrol commands, etc.

The PDCCH delivers information about resource allocation and a transportformat for a downlink shared channel (DL-SCH), information aboutresource allocation and a transport format for an uplink shared channel(UL-SCH), paging information of a paging channel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher layer control message such as a random access responsetransmitted on the PDSCH, a set of transmit power control commands forindividual UEs of a UE group, Tx power control commands, voice overInternet protocol (VoIP) activation indication information, etc. Aplurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted on an aggregate ofone or more consecutive control channel elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE includes a plurality of resourceelement groups (REGs). The format of a PDCCH and the number of availablebits for the PDCCH are determined according to the number of CCEs. AneNB determines a PDCCH format according to DCI transmitted to a UE andattaches a cyclic redundancy check (CRC) to control information. The CRCis masked by an identifier (ID) (e.g. a radio network temporaryidentifier (RNTI)) according to the owner or use of the PDCCH. If thePDCCH is destined for a specific UE, the CRC may be masked by acell-RNTI (C-RNTI) of the UE. If the PDCCH carries a paging message, theCRC thereof may be masked by a paging ID (P-RNTI). If the PDCCH carriessystem information (particularly, a system information block (SIB)), theCRC thereof may be masked by a system information RNTI (SI-RNTI). If thePDCCH is designated as a random access response, the CRC thereof may bemasked by a random access-RNTI (RA-RNTI).

FIG. 10 illustrates the structure of a UL subframe in an LTE system.

Referring to FIG. 10, a UL subframe includes a plurality of (e.g. 2)slots. A slot may include a different number of SC-FDMA symbolsaccording to CP length. The UL subframe is divided into a control regionand a data region in the frequency domain. The data region includes aPUSCH to transmit a data signal such as voice and the control regionincludes a PUCCH to transmit UCI. The PUCCH occupies a pair of RBs atboth ends of the data region in the frequency domain and the RB pairfrequency-hops over a slot boundary.

The PUCCH may deliver the following control information.

-   -   SR: SR is information requesting UL-SCH resources and is        transmitted using on-off keying (OOK).    -   HARQ ACK/NACK: HARQ ACK/NACK is a response signal to a DL data        packet received on a PDSCH, indicating whether the DL data        packet has been successfully received. 1-bit ACK/NACK is        transmitted as a response to a single DL codeword and 2-bit        ACK/NACK is transmitted as a response to two DL codewords.    -   CSI: CSI is feedback information regarding a DL channel. CSI        includes a CQI and multiple input multiple output (MIMO)-related        feedback information includes an RI, a PMI, a precoding type        indicator (PTI), etc. The CSI occupies 20 bits per subframe.

The amount of UCI that the UE may transmit in a subframe depends on thenumber of SC-FDMA symbols available for transmission of controlinformation. The remaining SC-FDMA symbols except for SC-FDMA symbolsallocated to RSs in a subframe are available for transmission of controlinformation. If the subframe carries an SRS, the last SC-FDMA symbol ofthe subframe is also excluded in transmitting the control information.The RSs are used for coherent detection of the PUCCH.

Hereinafter, a UL RS will be described. The UL RS supports ademodulation reference signal (DM-RS) associated with PUSCH/PUCCHtransmission and a sounding reference signal (SRS) not associated withPUSCH/PUCCH transmission. In this case, for the DM-RS and the SRS, thesame base sequence set is used.

Generation of an RS sequence will be described first. A UL RS is definedby a cyclic shift of a base sequence according to a predetermined rule.For example, an RS sequence r_(u,v) ^((α))(n) is defined by a cyclicsequence a of a base sequence r _(u,v)(n) according to the followingequation.

r _(u,v) ^((α))(n)=e ^(jαn) r _(u,v)(n), 0≦n<M _(sc) ^(RS)  [Equation12]

Here, M_(sc) ^(RS)=mN_(sc) ^(RB) is the length of the RS sequence and1≦m≦N_(RB) ^(max,UL). N^(max,UL) _(RB) represented by a multiple of aninteger of N_(RBsc) refers to a widest UL bandwidth configuration. Aplurality of RS sequences may be defined from one base sequence throughdifferent cyclic shift values α. A plurality of base sequences isdefined from a DM RS and an SRS. For example, the base sequences may bedefined using a root Zadoff-Chu sequence. The base sequences r _(u,v)(n)are divided into groups, each of which includes one or more basesequences. For example, each base sequence group may include one basesequence (v=0) having a length of M_(sc) ^(RS)=mN_(sc) ^(RB) (1≦m≦5) andtwo base sequences each having a length of M_(sc) ^(RS)=mN_(sc) ^(RB)(6≦m≦N_(RB) ^(max,UL)). In r _(u,v)(n), uε{0, 1, . . . , 29} denotes agroup number (i.e., group index) and v denotes a base sequence number(i.e., base sequence index) in the corresponding group. Each basesequence group number and a base sequence number in the correspondinggroup may vary with time.

The sequence group number u in a slot n_(s) is defined by a grouphopping pattern f_(gh)(n_(s)) and a sequence shift pattern f_(ss)according to the following equation.

u=(f _(gh)(n _(s))+f _(ss))mod 30  [Equation 13]

A plurality of different hopping patterns (e.g., 17 hopping patterns)and a plurality of different sequence shift patterns (e.g., 30 sequenceshift patterns) are present. Sequence group hopping may be enabled ordisabled according to a cell-specific parameter provided by a higherlayer.

The group hopping pattern f_(gh)(n_(s)) may be given for a PUSCH and aPUCCH according to the following equation.

$\begin{matrix}{{f_{gh}\left( n_{s} \right)} = \left\{ \begin{matrix}0 & \begin{matrix}{{if}\mspace{14mu} {group}\mspace{14mu} {hopping}} \\{{is}\mspace{14mu} {disabled}}\end{matrix} \\{\left( {\sum_{i = 0}^{7}{{c\left( {{8n_{s}} + i} \right)} \cdot 2^{i}}} \right){mod}\; 30} & \begin{matrix}{{if}\mspace{14mu} {group}\mspace{14mu} {hopping}} \\{{is}\mspace{14mu} {enabled}}\end{matrix}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack\end{matrix}$

Here, a pseudo-random sequence c(i) is given by Equation 15.

c(n)=(x ₁(n+N _(C))+x ₂(n+N _(C)))mod 2

x ₁(n+31)=(x ₁(n+3)+(n))mod 2

x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2  [Equation 15]

A pseudo-random sequence generator is initialized with c_(init) at thebeginning of each radio frame according to the following equation.

$\begin{matrix}{c_{init} = \left\lfloor \frac{n_{ID}^{RS}}{30} \right\rfloor} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

According to the current 3GPP LTE(-A) standards, the hopping pattern isthe same for a PUCCH and a PUSCH according to Equation 14 but thesequence shift pattern differs between the PUCCH and the PUSCH. Asequence shift pattern f_(ss) ^(PUCCH) for the PUCCH is provided basedon a cell ID according to the following equation.

f _(ss) ^(PUCCH) =n _(ID) ^(RS) mod 30  [Equation 17]

A sequence shift pattern f_(ss) ^(PUCCH) for the PUSCH is givenaccording to the following equation using the sequence shift patternf_(ss) ^(PUCCH) for the PUCCH and a value Δ_(ss) configured by a higherlayer.

f _(ss) ^(PUSCH)=(N _(ID) ^(cell)+Δ_(ss))mod 30  [Equation 18]

Here, Δ_(SS)ε{0, 1, . . . , 29}.

Base sequence hopping is applied only to RSs having a length M_(sc)^(RS)≧6N_(sc) ^(RB). For RSs having a length of M_(sc) ^(RS)≧6N_(sc)^(RB), the base sequence number v in a base sequence group is 0. For RSshaving a length of M_(sc) ^(RB)≧6N_(sc) ^(RB), the base sequence numberv in a base sequence group in a slot n_(s) is defined by Equation 19 ifgroup hopping is disabled and sequence hopping is enabled.

$\begin{matrix}{v = \left\{ \begin{matrix}{c\left( n_{s} \right)} & \begin{matrix}{{if}\mspace{14mu} {group}\mspace{14mu} {hopping}\mspace{14mu} {is}\mspace{14mu} {disabled}\mspace{14mu} {and}} \\{{sequence}\mspace{14mu} {hopping}\mspace{14mu} {is}\mspace{14mu} {enabled}}\end{matrix} \\0 & {otherwise}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

Here, the pseudo-random sequence c(i) is given by Equation 15. Thepseudo-random sequence generator is initialized with c_(init) accordingto Equation 20 at the beginning of each radio frame.

$\begin{matrix}{c_{init} = {{\left\lfloor \frac{n_{ID}^{RS}}{30} \right\rfloor \cdot 2^{5}} + f_{ss}^{PUSCH}}} & \left\lbrack {{Equation}\mspace{14mu} 20} \right\rbrack\end{matrix}$

For generation of a sequence, a method of determining a virtual cellidentity (ID) will now be described. In generating the sequence, n_(ID)^(RS) is defined according to a transmission type.

In association with PUSCH transmission, if a value for n_(ID) ^(PUSCH)is not set by higher layers or if PUSCH transmission corresponds to arandom access response grant or retransmission of the same transportblock as part of a contention based random access procedure, then n_(ID)^(RS)=N_(ID) ^(cell) and, otherwise, n_(ID) ^(RS)=n_(ID) ^(PUSCH).

In association with PUCCH transmission, if a value for n_(ID) ^(PUCCH)is not set by higher layers, then n_(ID) ^(RS)=N_(ID) ^(cell) and,otherwise, n_(ID) ^(RS)=n_(ID) ^(PUSCH).

In association with SRS transmission, n_(ID) ^(RS)=n_(ID) ^(cell).

In association with a DM-RS, a PUSCH RS sequence will now be described.

A PUSCH DM-RS sequence r_(PUSCH) ^((λ))(•) associated with a layer λε{0,1, . . . , υ−1} may be defined by Equation 21.

r _(PUSCH) ^((λ))(m·M _(sc) ^(RS) +n)=w ^((λ))(m)r _(u,c) ^((α) ^(λ)⁾(n)

m=0,1

where n=0, . . . ,M _(sc) ^(RS)−1 and M _(sc) ^(RS) =M _(sc)^(PUSCH).  [Equation 21]

In relation to RS sequence generation, a sequence r_(u,v) ^((α) ^(λ)⁾(0), . . . , r_(u,v) ^((α) ^(λ) ⁾(M_(sc) ^(RS)−1) is defined. Anorthogonal sequence w^((λ))(m)) is given by [w^(λ)(0) w^(λ)(1)]=[1 1]for DCI format 0 if a higher layer parameter “Activate-DMRS-with OCC” isnot set or if a temporary C-RNTI has been used to transmit the mostrecent UL-related DCI for a transport block associated withcorresponding PUSCH transmission and, otherwise, the orthogonal sequencew^((λ))(m) is given by Table 5 using a cyclic shift field in the mostrecent UL-related DCI for a transport block associated withcorresponding PUSCH transmission.

TABLE 5 Cyclic Shift Field in uplink-related DCI n_(DMRS,λ) ⁽²⁾[w^((λ))(0) w^((λ))(1)] format λ = 0 λ = 1 λ = 2 λ = 3 λ = 0 λ = 1 λ = 2λ = 3 000 0 6 3 9 [1 1] [1 1] [1 −1] [1 −1] 001 6 0 9 3 [1 −1] [1 −1] [11] [1 1] 010 3 9 6 0 [1 −1] [1 −1] [1 1] [1 1] 011 4 10 7 1 [1 1] [1 1][1 1] [1 1] 100 2 8 5 11 [1 1] [1 1] [1 1] [1 1] 101 8 2 11 5 [1 −1] [1−1] [1 −1] [1 −1] 110 10 4 1 7 [1 −1] [1 −1] [1 −1] [1 −1] 111 9 3 0 6[1 1] [1 1] [1 −1] [1 −1]

A cyclic shift α_(λ) in a slot n_(s) is given as α_(λ)=2πn_(cs,λ)/12where n_(cs,λ)=(n_(DMRS) ⁽¹⁾+n_(DMRSλ) ⁽²⁾+n_(PN)(n_(s)))mod 12.n_(DMRS) ⁽¹⁾ is given by Table 6 according to a parameter cyclicShiftprovided by higher layers. Table 6 shows mapping of cyclicShift given byhigher layers to n_(DMRS) ⁽¹⁾.

TABLE 6 cyclicShift n_(DMRS) ⁽¹⁾ 0 0 1 2 2 3 3 4 4 6 5 8 6 9 7 10

n_(DMRSλ) ⁽²⁾ is given by a cyclic shift for a DM-RS field in mostrecent UL-related DCI for a transport block associated withcorresponding PUSCH transmission and a value of n_(DMRSλ) ⁽²⁾ is givenin Table 5.

The first row of Table 5 should be used to obtain n_(DMRSλ) ⁽²⁾ andw^((λ))(m) if there is no most recent UL-related DCI for the sametransport block associated with corresponding PUSCH transmission, and i)if an initial PUSCH for the same transport block is semi-persistentlyscheduled or ii) if the initial PUSCH is scheduled by a random accessresponse grant.

n_(PN)(n_(s)) is given by Equation 22.

n _(PN)(n _(s))=Σ_(i=0) ⁷(8N _(symb) ^(UL) ·n _(s) +i)·2^(i)  [Equation22]

where a pseudo-random sequence c(i) is given by Equation 15. c(i) iscell-specific. A pseudo-random sequence generator is initialized withc_(init). c_(init) is given by Equation 23.

$\begin{matrix}{c_{init} = {{\left\lfloor \frac{N_{ID}^{cell}}{30} \right\rfloor \cdot 2^{5}} + \left( {\left( {N_{ID}^{cell} + \Delta_{ss}} \right){mod}\; 30} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 23} \right\rbrack\end{matrix}$

where Equation 23 is applied when a value for N_(ID) ^(csh) ^(_) ^(DMRS)is not set by higher layers or if PUSCH transmission corresponds to arandom access response grant or retransmission of the same transportblock as part of a contention based random access procedure and Equation24 is applied in the other cases.

$\begin{matrix}{c_{init} = {{\left\lfloor \frac{N_{ID}^{{csh}\_ {DMRS}}}{30} \right\rfloor \cdot 2^{5}} + \left( {N_{ID}^{{csh}\_ {DMRS}}{mod}\; 30} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 24} \right\rbrack\end{matrix}$

The vector of RSs is precoded according to Equation 25.

$\begin{matrix}{\begin{bmatrix}{\overset{\sim}{r}}_{PUSCH}^{(0)} \\\vdots \\{\overset{\sim}{r}}_{PUSCH}^{({P - 1})}\end{bmatrix} = {W\begin{bmatrix}r_{PUSCH}^{(0)} \\\vdots \\r_{PUSCH}^{({v - 1})}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 25} \right\rbrack\end{matrix}$

where P is the number of antenna ports used for PUSCH transmission.

For PUSCH transmission using a single antenna port, P=1, W=1, and υ=1.For spatial multiplexing, P=2 or P=4 and a precoding matrix W should bedistinguished from a precoding matrix used for precoding of a PUSCH inthe same subframe.

Hereinafter, a detailed method of performing D2D communication when D2Dcommunication is introduced to a wireless communication system (e.g.,3GPP LTE system or 3GPP LTE-A system) will be described based on theabove description.

FIG. 11 is a diagram for conceptually explaining D2D communication. FIG.11(a) illustrates a conventional eNB-centered communication scheme inwhich a first UE UE1 may transmit data to an eNB on UL and the eNB maytransmit data received from the first UE UE1 to a second UE UE2 on DL.

FIG. 11(b) illustrates a UE-to-UE communication scheme, as an example ofD2D communication, in which UEs may exchange data without passingthrough an eNB. A link directly established between devices may bereferred to as a D2D link. D2D communication has advantages of decreasein latency compared with the conventional eNB-centered communicationscheme and reduction in necessary radio resources

Although D2D communication supports communication between devices (orUEs) without passing through an eNB, since resources of a legacywireless communication system (e.g., 3GPP LTE/LTE-A) are reused for D2Dcommunication, D2D communication should not generate interference ordisturbance with the legacy wireless communication system. In the samecontext, it is also important to minimize interference to which D2Dcommunication is subjected by a UE and an eNB operating in the legacywireless communication system.

The present invention proposes transmission timings of a D2Dsynchronization signal (D2DSS) and a physical D2D synchronizationchannel (PD2DSCH) transmitted by D2D transmission (Tx) UEs performingD2D communication and a method of transmitting the D2DSS and thePD2DSCH.

The D2DSS is transmitted as a predetermined signal for synchronizationof D2D communication and a reception (Rx) UE detects timesynchronization and frequency synchronization by blind-detecting theD2DSS. The PD2DSCH informs a UE of basic information used for D2Dcommunication (e.g., channel bandwidth, information about a subframe inwhich D2D communication is performed, a resource pool for schedulingassignment (SA), and the like) and is transmitted by coding (e.g., turbocoding or convolutional coding) a data payload.

When a D2D UE detects the D2DSS, since synchronization is usuallymaintained for about 500 ms, a transmission period of the D2DSS may be amaximum of a few hundred ms. For convenience of description, it isassumed in the present invention that the D2DSS is transmitted at aperiod of 100 ms.

FIG. 12 is a diagram referenced to illustrate basic transmission timingsof a D2DSS and a PD2DSCH. Referring to FIG. 12, since informationincluded in the PD2DSCH indicates infrequently varying values, thevalues are changed at a slow period (e.g., seconds). That is, in FIG.12, a PD2DSCH that an Rx UE receives at t=0 ms and a PD2DSCH that the RxUE receives at t=100 ms may be regarded as almost the same information.Therefore, the Rx UE does not need to re-receive the PD2DSCH for apredetermined time after successfully receiving the PD2DSCH.

For another reason, in order for an unspecified UE to detect the D2DSSor the PD2DSCH at an arbitrary time, a Tx UE may transmit the D2DSS orthe PD2DSCH at a short period (e.g., the D2DSS or the PD2DSCH may betransmitted at a shorter period than the 100 ms illustrated in FIG. 12)and a UE (particularly, an idle mode UE) desirably performs a detectionoperation only for a part of the transmitted D2DSS and PD2DSCH, for thepurpose of energy saving.

Accordingly, the present invention proposes a method in which the periodof the PD2DSCH consists of a main period and a sub period and thePD2DSCH is repeated at the sub period within the main period (in thiscase, the contents of the PD2DSCH between main periods may not bechanged).

For convenience of description, it will be assumed hereinbelow that anew PD2DSCH is transmitted at an interval of two seconds (2000 ms) (asin FIG. 13 which will be described later). That is, the contents of thePD2DSCH are changed at a period of two seconds. However, this assumptionis purely for convenience of description and the present inventionshould not be limited to the above-described period. For example, thepresent invention may be applied in a situation in which the PD2DSCH hasa period slower than the D2DSS. Therefore, after receiving the PD2DSCH,a UE may indirectly recognize a subframe number (SFN) based on thePD2DSCH.

1. Chase Combining for D2D Communication

According to an embodiment of the present invention, as a case oftransmitting the PD2DSCH at a sub period, the same signal may berepeatedly retransmitted so as to cause an Rx UE to accumulate energy ofthe signal through chase combining.

For example, when the same transmission structure as in FIG. 12 is used,the Rx UE may accumulate energy starting from the first received PD2DSCHand stop a PD2SCH reception operation starting from a decoding successtiming until the start of the next main period, thereby reducing powerconsumption of the UE.

While chase combining is performed, since all PD2DSCH signals are thesame, it cannot be determined at which location of a main period or asub period a signal is present. In this case, a method of determiningthe period of a PD2DSCH is as follows (for a frame number or a subframenumber, numbering based on a legacy network may be used or a new frameor subframe number defined for D2D communication may be used).

A main period and a sub period may be predefined as specific fixedvalues. That is, the main period and the sub period may be determined inlinkage with a frame/subframe number. (e.g., if (frame number)%100=0,then this means that a new main period is started and, if (framenumber)%10=0, then this means that new sub period is started)

The main period and the sub period may be indicated by a root sequenceof a D2DSS. This method is effective for an out-NW UE, a partial-NW UE,or a UE performing inter-cell D2D communication. That is, the mainperiod and the sub period may be determined by a sequence number and astart timing of each period may be indicated by a frame number, etc. Forexample, if (sequence number)/4=A, then the main period and sub periodmay be predefined according to A or may be transmitted to a UE throughhigher layer signaling.

The main period and the sub period may be configured by an eNB through ahigher layer signal (e.g., a D2D SIB in an RRC signal). This method maybe used with respect to an in-network (in-NW) UE.

Using the above-described methods, a UE recognizes the main period andthe sub period and re-detects the PD2DSCH at a period at which thePD2DSCH is reset (i.e., the main period, for example, 2 seconds (s)). Inthis case, a detailed operation is as follows.

A UE attempts to detect the PD2DSCH after the main period starting froma detection start timing of the PD2DSCH. In this case, the UE does notaccurately detect the start of the next period and is aware of onlywhether the PD2DSCH is present at a corresponding timing (e.g.,subframe).

A UE may be aware of a current frame number by receiving frame numberinformation through a higher layer signal (e.g., a D2D SIB in an RRCsignal) received from an eNB and may be aware of the start timing of thenext main period using period information obtained through theabove-described method capable of determining the period of the PD2DSCH.Therefore, the UE may monitor the PD2DSCH at the start timing of thenext main period.

2. Incremental Redundancy (IR) for D2D Communication

As another embodiment for transmitting the PD2DSCH at a sub periodaccording to the present invention, turbo coding or convolutional codingis performed using different redundancy version (RV) values, therebyraising the reception rate of an Rx UE through an incremental redundancy(IR) scheme.

FIG. 13 is a diagram referenced to illustrate the main period and subperiod of a PD2DSCH. Referring to FIG. 13, a total of 4 RV values ischanged in order of {0, 2, 1, 3}.

A UE may recognize a specific timing within a sub period by blinddetecting the RV value of the PD2DSCH. In particular, since thestructure of the PD2DSCH proposed in the present invention isself-decodable, decoding may be performed even when only one ofsuccessive PD2DSCHs is received. If a signal-to-noise ratio (SNR) isinsufficient, decoding may be performed by connecting multiple PD2DSCHs.

Furthermore, the UE may perform an operation according to the PDSCHperiod recognition method described in “1. Chase Combining for D2DCommunication” and the contents of described in the next PD2DSCHreception method. Therefore, the operation of the UE is replaced withthe above description.

If frame number information is received through a higher layer signal ora D2DSS, the number of bits of the frame number information may bedecreased because partial information about a frame number has beenderived through an RV value.

FIG. 14 is a diagram referenced to explain a method of indicating aframe number varying with whether an RV is present according to thepresent invention.

Similarly, in this method (i.e., an IR scheme), a frame index mayrepresent i) an existing radio frame index, ii) a D2D frame index or aD2D subframe index, or particularly iii) a D2D synchronizationframe/subframe index out of the D2D frame. In addition, the D2D frameindex may be an index which is counted independently of the existingradio frame index.

Meanwhile, when using the IR scheme, if there are too many RV values,blind decoding complexity of a UE is excessively increased. Therefore,the present invention proposes the following RV indication method.

An RV value may be accurately indicated or a set of RV values may beindicated by sequence information or a symbol location of a D2DSS.

Prior to decoding a PD2DSCH, an RV value or a set of RV values may beindicated by a sequence of a D2D DM-RS used for channel estimation or acyclic shift (CS) of the D2D DM-RS.

In both the chase combining and IR schemes, part of a sub period may beomitted for power saving of a transmitter.

FIG. 15 is a diagram referenced to explain omission of PD2DSCHtransmission in part of a sub period according to the present invention.In FIG. 15, a PD2DSCH is transmitted only at the first sub period andtransmission of the PD2DSCH is omitted at the next sub period. Even inthis case, the chase combining or IR scheme may be applied. A PD2DSCHreceived at an n-th period may indicate a D2D setting value of an(n+1)-th period rather than a D2D setting value of a current period.That is, a received PD2DSCH value is not applied immediately but may beapplied as a changed setting value beginning from a start timing of the(n+1)-th period after a predetermined time to guarantee a combiningdecoding delay.

Further, in the above chase combining and IR schemes, it has beenassumed that a UE receives a new PD2DSCH at every main period. However,a PD2DSCH having the same contents may be maintained during multiplemain periods and, in this case, a monitoring operation of an Rx UE isnot needed.

Accordingly, in the present invention, a PD2DSCH update notificationsignal may be additionally transmitted. That is, upon receiving theupdate notification signal, a UE starts to monitor a PD2DSCH at thebeginning of the next main period. The update notification signal may beindicated through an additional update notification field of a pagingsignal of an eNB to an Rx UE in network coverage (i.e., in-NW Rx UE).Therefore, upon receiving a signal indicating D2D traffic from the eNB,a UE in a D2D idle state may be switched to an active state.

Alternatively, the PD2DSCH update notification signal may be indicatedusing different root sequences or symbol locations according to whetherupdate is performed or not in a D2DSS and this method may be used withrespect to both an in-NW Rx UE and an out-NW Rx UE.

A paging signal of the present invention may have a structure in whichthe PD2DSCH update notification field is added to an existing cellularpaging signal but a D2D paging signal may be separately configured andmay be transmitted at a separate period from the cellular paging signal.In this case, the D2D paging signal may indicate not only whether aPD2DSCH signal is updated but also whether a control information (CI)signal transmitted in the form of piggybacking on a data communicationchannel is updated. The CI signal includes information about a new dataindicator (NDI) or an RV and whether the CI signal is updated may beindicated by the paging signal. Herein, CI may mean CI used for D2Dcommunication or a channel for CI.

FIG. 16 illustrates CI piggybacking according to the present invention.In FIG. 16, it is assumed that resources except for an RS and CI areused for data communication.

A PD2DSCH change notification using a paging signal will now bedescribed with reference to FIG. 17. In FIG. 17, a UE is synchronizedwith a D2DSS at an n-th main period and decodes two received PD2DSCHs.Next, since the UE has not received an additional paging notification,the UE continues to receive only the D2DSS and updates synchronization.However, upon receiving the change notification at an (n+1)-th mainperiod, the UE may recognize that a new PD2DSCH is transmitted at an(n+2)-th main period and start to receive the PD2DSCH.

3. Repetition Count for D2D Communication

According to an embodiment of the present invention, a repetition countmay be added as one of contents transmitted in a PD2DSCH. For example, aUE that is aware of a main period determined by higher layer signalingor a predefined main period (e.g., by the above-described methods) maybe aware of at which timing the next PD2DSCH is to be detected accordingto a repetition count field value by decoding the PD2DSCH.

For example, if a period at which the contents of the PD2DSCH arechanged is 2 seconds and if the PD2DSCH is transmitted every 100 ms,when the repetition count field is 16 as a result that the UE decodesthe PD2DSCH at an arbitrary timing, the PD2DSCH may be detected after400 ms. In this case, it may be regarded that main contents of thePD2DSCH (e.g. information except for the repetition count) are notchanged up to the corresponding timing.

4. CRC Mask Setting of SS for D2D Communication

Hereinafter, a CRC mask setting method of an SS when UEs performing D2Dcommunication perform synchronization therebetween according to thepresent invention will be described.

FIG. 18 and FIG. 19 are diagrams referenced to explain the basestructure of an SS associated with D2D communication to which thepresent invention is applied. In FIG. 18, a PD2DSS denotes a primary D2Dsynchronization signal, an SD2DSS denotes a secondary D2Dsynchronization signal, and a PD2DSCH denotes a physical D2Dsynchronization channel. An SS for D2D communication includes the abovethree signals PD2DSS, SD2DSS, and PD2DSCH which have the same form asthe structures of a PSS, SSS, and a PBCH in an LTE system, respectively.

Such SSs may be used in a D2D connection state as in FIG. 19. A basicconnection state of a D2D synchronization procedure will now bedescribed with reference to FIG. 19.

First, a synchronization source (SR) may be an eNB or a UE. The SR maytransmit an independent SS. For example, the eNB as the SR may transmita PSS/SSS. Therefore, a UE performing D2D communication (e.g., UE3) mayreceive an SS and perform D2D communication. Meanwhile, relay UEs mayreceive an SS of the SR and retransmit the SS to other D2D UEs.

In this case, a CRC may be attached to a data field of a PD2DSCH and thePD2DSCH may be transmitted by performing encoding using turbo orconvolutional codes (e.g. turbo coding or convolutional coding). In thepresent invention, such a CRC may be masked to transmit specificimportant information. Hereinafter, for convenience of description, CRClength is exemplified as 16 bits but other values may be used for CRClength.

According to the present invention, type information of an SR (e.g., SRUE) may be indicated by a CRC mask. That is, when a plurality of SSs isreceived, an index indirectly indicating accuracy of synchronization maybe included in the CRC mask to serve as a reference in determiningpriority of communication. Table 7 shows an example in which informationabout an SR type is included in the CRC mask. In addition, even when aUE transmits a D2DSS/PD2DSCH, the SR type may differ according towhether the UE is in eNB coverage or out of eNB coverage. This isbecause an ultimate SR is an eNB when the UE is in eNB coverage.Accordingly, in the above description, if the SR type is the eNB, thismay mean that the UE transmitting the D2DSS/PD2DSCH is in eNB coverage.That is, whether the UE transmitting the D2DSS/PD2DSCH is in eNBcoverage or out of eNB coverage may be distinguished through the CRCmask.

TABLE 7 SR type CRC mask eNB 0x0000 Out-NW UE 0xFFFF

According to the present invention, the CRC mask may indicate a stratumlevel. That is, the CRC mask may indicate how many times a received SSis retransmitted. Generally, a synchronization error is accumulated as arelaying operation is performed. To avoid this phenomenon, it isdesirable to limit the number of times of relaying of an SS.

For example, when the stratum level is defined as in Table 8, if astratum level is 0, this means that the SS is directly transmitted by anSR UE and, if the stratum level is 1, this means that the SS is a signalwhich is relayed once, i.e., the SS is transmitted by a relay (e.g.,Relay1 or Relay2) in FIG. 19.

TABLE 8 Stratum level CRC mask 0 0x0000 1 0xFFFF 2 0x1111

In the example of Table 8, it is assumed that a maximum value of thestratum level is 2. The stratum level of 2 may mean that the SS is nolonger relayed.

Meanwhile, a D2DSS of an eNB is an LTE PSS/SSS not including a PD2DSCH.That is, the stratum level of 0 will be always used only by an out-NW SRUE. Therefore, since accuracy of the SS may be indirectly recognized,the CRC mask may be a reference for determining priority when multipleSSs are detected.

According to the present invention, the CRC mask may indicate atransmission type. That is, whether the transmission type is unicast,groupcast, or broadcast may be indicated through the CRC mask.Therefore, UEs that desire to receive broadcast information may decodethe PD2DSCH using a mask corresponding to broadcast and, if decoding issuccessful, the UEs may perform the next operation (e.g., discoverysignal reception) and, if the UEs fail to perform decoding, the UEs maydetect another broadcast signal.

According to the present invention, the CRC mask may indicate a PD2DSCHformat indicator. Information necessary for a UE may differ according toi) whether the UE is in-NW or out-NW, ii) unicast, groupcast, orbroadcast type of D2D communication, or iii) other reasons or it may bedesirable to receive some information from an eNB (rather than a UEperforming D2D communication). For example, in a situation in which a UEis in a network (i.e., in-NW), it is desirable that the eNB directlydesignate all resource pools directly in terms of entire resourcescheduling.

Therefore, the UE may receive an in-NW resource pool field from the eNBthrough a higher layer signal (e.g., RRC) and delete a PD2DSCH resourcepool field. Instead, another field value may be repeated or a reservedfield may be further secured. That is, in various situations, a type ofinformation included in the PD2DSCH may vary and the CRC mask may beused to indicate the information type.

FIG. 20 is a diagram referenced to explain the case in which a CRC maskis used as a PD2DSCH format indicator according to the presentinvention.

As indicated in FIG. 20, assuming that different formats of PD2DSCHs aretransmitted, Field D may be omitted in Formats 1 and 2 and Field B maybe omitted in Formats 1A and 2A.

Therefore, a D2D Rx UE receiving a PD2DSCH may blind decode the PD2DSCHto two length types of Format 1/1A and Format 2/2A and perform CRC usingtwo CRC demasking types (0x0000 and 0xFFFF), thereby recognizing thePD2DSCH as a successful format. While two length types are exemplarilyblind detected to clarify description, this is purely an additionalelement and the present invention is applicable to only one length(i.e., only a CRC mask is checked).

In addition, the CRC mask according to the present invention mayindicate a synchronization reference ID. That is, each synchronizationreference may include an ID to distinguish from other references.Hereinafter, the ID for distinguishing between synchronizationreferences will be referred to as a synchronization reference ID.

For example, UEs, such as Relay1 and Relay2 of FIG. 19, that relay aD2DSS of another UE, may use the same synchronization reference as theUE that has originally transmitted the D2DSS and, therefore, have thesame synchronization reference ID.

Generally, a sequence of a D2DSS is generated from a synchronizationreference ID (e.g., a sort of a virtual cell ID having the samestructure as an existing LTE cell ID). If a CRC of a PD2DSCH isgenerated from the synchronization reference ID, a UE may confirmwhether the synchronization reference ID derived from detection of theD2DSS has been actually transmitted. In addition, if an SR ID differsaccording to the above-described SR type, the SR ID may be used for CRCmaking so that the SR type may be considered for CRC masking. Forexample, an even-numbered SR ID may be interpreted as the case in whichan eNB is an SR and an odd-numbered SR ID may be interpreted as the casein which a UE is an SR. The even-numbered SR ID may be interpreted as anID when a UE located in an eNB transmits the D2DSS and the odd-numberedSR ID may be interpreted as an ID when a UE out of an eNB transmits theD2DSS. Similarly, if an SR ID of a predetermined region is used by a UEthat transmits the D2DSS according to an instruction of an eNB and an SRID of other regions is used by a UE out of coverage without aninstruction of the eNB, when a CRC mask is derived through the SR ID, aUE receiving the PD2DSCH may recognize, through the CRC mask, in whichsituation of a UE the D2DSS is transmitted.

The CRC mask according to the present invention may be used to indicatea CP length. That is, a UE performing D2D communication using the samesynchronization reference needs to adjust the CP length. In this case,instead of additional signaling through the PD2DSCH, the CP length maybe indicated through the CRC mask.

The CRC mask according to the present invention may also be used toindicate a synchronization resource index. Namely, multiplesynchronization resources may be used by a UE to transmit the D2DSS. Forexample, if a period of the D2DSS transmitted by one UE is given as 40ms, a plurality of synchronization resources is present in one period of40 ms and one UE in one period may transmit the D2DSS on onesynchronization resource and receive a D2DSS transmitted by another UEon another synchronization resource.

Therefore, when a UE receives a specific D2DSS and PD2DSCH, an index ofa synchronization resource may be indicated through the CRC mask of thePD2DSCH in order to determine the location of a synchronization resourceon which a corresponding signal is received within a period of theD2DSS.

FIG. 21 is a diagram referenced to explain the case in which an index ofa synchronization resource is indicated through a CRC mask according tothe present invention. In FIG. 21, two synchronization resources areadjacent to each other in one D2DSS period and the other time resourcesare used to transmit and receive a D2D signal and a cellular signal. Inthis case, if a specific UE receives a D2DSS/PD2DSCH on a specificsynchronization resource, the UE should be aware of an index of thecorresponding signal to identify the location of another synchronizationresource, thereby performing D2D transmission and reception, Forexample, the specific UE receives the D2DSS/PD2DSCH on the specificsynchronization resource, identifies an index of the signal, andtransmits a D2DSS on a synchronization resource different from theidentified specific synchronization resource, thereby avoiding collisionwith the D2DSS received thereby.

That is, in FIG. 21, upon receiving the D2DSS/PD2DSCH on the specificsynchronization resource, if the UE is aware that an index of thecorresponding synchronization resource is 0 through the CRC mask, the UEmay recognize that another synchronization resource having an index of 1is present immediately after the specific synchronization resource.Alternatively, if the index of the specific synchronization resource is1, the UE may recognize that another synchronization resource having anindex of 0 is present immediately prior to the specific synchronizationresource.

In this way, the operation indicating the synchronization resource indexusing the CRC mask is similar to the operation indicating theabove-described stratum level. In the case of general synchronizationrelaying described in FIG. 19, since a UE of a specific stratum levelshould receive a D2DSS of a previous level, synchronization resources ofdifferent stratum levels should be distinguished in the time domain.Accordingly, in synchronization relaying using a stratum level, apredetermined linkage may be present between a synchronization resourceindex and a stratum level. In this case, the operation of indicating thesynchronization resource index through the CRC mask may be identical tothe operation indicating the stratum level. However, the stratum levelmay not be signaled according to a specific form of a D2Dsynchronization operation. In particular, for a UE moving at a highspeed, since the stratum level is continuously changed, use of thestratum level may cause frequent synchronization change, therebydeteriorating overall performance Thus, even if the stratum level is notused, since an individual UE should receive a D2DSS of another UE whiletransmitting a D2DSS, synchronization resources still need to bedistinguished in the time domain and, in this case, the synchronizationresource index needs to be indicated to enable the above-describedoperation.

In performing CRC masking for a PD2DSCH, it is possible to generate afinal bit string to be used for CRC masking by combining at least two ofthe above-described SR (e.g., SR UE) type, stratum level, transmissiontype, PD2DSCH format indicator, synchronization reference ID, CP length,and synchronization resource index.

Meanwhile, the above-described information is used not only for CRCmasking but also for generation of i) a sequence of scrambling a databit of a PD2DSCH or ii) a sequence of an RS of demodulating the PD2DSCH,thereby enabling transmission of the information to a UE using widervariety of methods. That is, the above-described information is used togenerate various sequences for transmission of the PD2DSCH and istransmitted to an Rx UE.

According to the above description, a receiver may restore an originalbit value by performing decoding (convolutional decoding or turbodecoding) and then use a corresponding information value when there areno errors as a result of checking a mask value and CRC through CRC blinddecoding.

5. DM-RS Transmission Method for D2D Communication

Hereinafter, a method including the above-described information in aDM-RS associated with a synchronization channel for D2D communicationwill be described in more detail.

As described above, there are several elements for determining a DM-RSof a PUSCH but the most basically used element is n_(ID) ^(RS)corresponding to a cell ID (or a virtual cell ID which is set by anetwork independently of the cell ID).

Therefore, in D2D communication according to the present invention, aDM-RS may be generated by replacing an n_(ID) ^(RS) field withinformation to be transmitted. For example, the DM-RS may be generatedby inserting a synchronization reference ID into the cell ID.

Meanwhile, the region of the synchronization reference ID is wide,whereas only up to 30 base sequences of a PUSCH DM-RS are generated.Even if the DM-RS is generated by inserting the synchronizationreference ID into the place of the cell ID, D2DSSs/PD2DSCHs of differentsynchronization reference IDs may be frequently transmitted on the sameresource as the same DM-RS. In particular, in a state in which an Rx UEdoes not recognize a frame number or a subframe number, since it isimpossible to perform sequence hopping using the frame number or thesubframe number, the above-described restriction becomes severer. Inthis case, the problem may be relieved by generating a DM-RS generationparameter, for example, a DM-RS cyclic shift and/or an orthogonal covercode (OCC), using a synchronization reference ID.

For example, the OCC may be determined using partial lower bits of thesynchronization reference ID, the DM-RS cyclic shift may be determinedusing partial lower bits among the other bits except for the bits usedfor the OCC, and a sequence group number may be determined by replacingthe place of a base sequence generation parameter n_(ID) ^(RS) ordirectly, using bits other than the bits used for the OCC and the DM-RScyclic shift. For example, the OCC may be determined using one lower bitof the synchronization reference ID as indicated by Equation 26.

$\begin{matrix}\left\{ {\begin{matrix}\begin{bmatrix}{+ 1} & {+ 1}\end{bmatrix} & {{{if}\mspace{14mu} n_{ID}^{D\; 2{DSS}}{mod}\; 2} = 0} \\\begin{bmatrix}{+ 1} & {- 1}\end{bmatrix} & {{{if}\mspace{14mu} n_{ID}^{D\; 2{DSS}}{mod}\; 2} = 1}\end{matrix},} \right. & \left\lbrack {{Equation}\mspace{14mu} 26} \right\rbrack\end{matrix}$

The cyclic shift (CS) may be determined as Equation 27 by modifying anequation of a PUSCH DM-RS CS using three lower bits of thesynchronization reference ID.

n _(DMRS) ⁽¹⁾=0, n _(DMRS) ⁽²⁾ =└n _(ID) ^(D2DSS)/2┘ mod 8  [Equation27]

A base sequence may be determined as Equation 28 by modifying anequation of a PUSCH DM-RS base sequence directly using thesynchronization reference ID.

n _(ID) ^(RS) =n _(ID) ^(D2DSS) , f _(ss) ^(PSSCH) =n _(ID) ^(D2DSS) mod30  [Equation 28]

In Equation 28, n_(ID) ^(D2DSS) is the synchronization reference ID.Alternatively, since the OCC has been determined through the lowestsynchronization reference ID, the base sequence may be set such thatn_(ID) ^(RS)=└n_(ID) ^(D2DSS)/2┘, f_(ss) ^(PSSCH)=└n_(ID) ^(D2DSS)/2┘mod 30. In addition, since at least one of the CS and the OCC is set tothe four lower bits of the synchronization reference ID, the basesequence may be set such that n_(ID) ^(RS)=└n_(ID) ^(D2DSS)/2⁴┘, f_(ss)^(PSSCH)=└n_(ID) ^(D2DSS)/2⁴┘ mod 30. Conversely, the base sequence maybe determined using lower bits of the synchronization reference ID andthe CS/OCC may be determined using the other higher bits.

Since a synchronization resource index corresponds to information abouttime, the synchronization resource index may replace a subframe index(or slot index) corresponding to a time resource index in generating aDM-RS. For example, if two synchronization resources are present in oneD2DSS period, slot indexes on the first synchronization resource may beset to 0 and 1 and slot indexes on the second synchronization resourcemay be set to 2 and 3.

Hereinafter, scrambling of a PD2DSCH will be described. Currently, aninitial value of scrambling related to a PUSCH in LTE is set asindicated in Equation 29.

c _(init) =n _(RNTI)·2¹⁴ +q·2¹³ +└n _(s)/2┘·2⁹ +N _(ID)^(cell)  [Equation 29]

where n_(RNTI) is a value indicated by higher layer signaling, q is acodeword index, └_(s)/2┘ denotes a subframe number of data, and N_(ID)^(cell) is a cell ID. In the present invention, Equation 29 may bechanged to methods 29-1 to 29-7 to determine the initial value ofscrambling of the PD2DSCH.

-   -   29-1: In Equation 29, n_(RNTI) may be fixed to ‘0’.    -   29-2: In Equation 29, N_(ID) ^(cell) may be fixed to ‘510’ or        ‘511’.    -   29-3: In Equation 29, N_(ID) ^(cell) may be set to a        synchronization reference ID.    -   29-4: In Equation 29, n_(RNTI) may be set to a synchronization        reference ID.    -   29-5: In Equation 29, n_(RNTI) may be fixed to ‘510’ or ‘511’.    -   29-6: In Equation 29, n_(s) may be set to ‘0’.    -   29-7: In Equation 29, n_(s) may be determined by a subframe        number or a slot number in which a D2DSS is transmitted.

If method 29-2, 29-4, or 29-6 is used for scrambling according to thepresent invention, then c_(init)=n_(ID) ^(D2DSS)·2¹⁴+510 orc_(init)=n_(ID) ^(D2DSS)·2¹⁴+511. Since there is one codeword index inD2D communication, q is assumed to be 0. In this case, n_(ID) ^(D2DSS)is a synchronization reference ID.

If method 29-3, 29-5, or 29-6 is used for scrambling according to thepresent invention, then c_(init)=510·2¹⁴+n_(ID) ^(D2DSS) orc_(init)=511·2¹⁴+n_(ID) ^(D2DSS). Since there is one codeword in D2Dcommunication, q is assumed to be 0. In this case, n_(ID) ^(D2DSS) is asynchronization reference ID.

Meanwhile, in the case of D2DSSue_net, there may be D2DSSue_nettransmitted by an in-coverage UE based on a timing of an eNB as areference and D2DSSue_net transmitted by an out-coverage UE based onD2DSSue_net transmitted by the in-coverage UE as a timing reference. Inthis case, an indicator (e.g., 1-bit indicator) indicating whether a UEthat transmits D2DSSue_net is in coverage or out of coverage may betransmitted in a PD2DSCH.

In this case, even when D2DSSue_net has the same synchronization ID, itis necessary to differently configure scrambling and a DM-RS accordingto the state of a Tx UE (in-coverage/out-coverage) because the contentsof the PD2DSCH are changed by the 1-bit indicator. Therefore, thepresent invention proposes that a PD2DSCH and/or a DM-RS for decodingthe PD2DSCH be differently set by the 1-bit indicator.

For example, for the DM-RS, an OCC part may be determined by the 1-bitindicator. Then, n_(DMRS) ⁽²⁾ may be set to n_(ID) ^(D2DSS) mod 8. Inaddition, n_(DMRS) ⁽¹⁾ may be determined by the 1-bit indicator. ForDM-RS reconfiguration, n_(ID) ^(D2DSS) may be differently set by the1-bit indicator. For example, if the 1-bit indicator is 0, n_(ID)^(D2DSS) may be used and, if the 1-bit indicator is 1, n_(ID) ^(D2DSS)may be set to n_(ID) ^(D2DSS)+X (where X may be a preset value or apredetermined value linked with n_(ID) ^(D2DSS)).

For a scrambling sequence, methods 29-8 to 29-11 to which the 1-bitindicator is applied may be additionally considered.

-   -   29-8: In Equation 29, q is differently set according to the        1-bit indicator.    -   29-9: In Equation 29, n_(RNTI) may be differently set according        to the 1-bit indicator. For example, an in-coverage UE may use        510 as n_(RNTI) and an out-coverage UE may use 511 as n_(RNTI).    -   29-10: N_(ID) ^(cell) may be differently set according to the        1-bit indicator. For example, an in-coverage UE may use 510 as        N_(ID) ^(cell) and an out-coverage UE may use 511 as N_(ID)        ^(cell).    -   29-11: n_(s) may be differently set according to the 1-bit        indicator. For example, an in-coverage UE may use 0 as n_(s) and        an out-coverage UE may use another specific value other than 0        as n_(s).

FIG. 22 illustrates a BS and a UE that are applicable to an embodimentof the present invention. If a wireless communication system includes arelay, communication in a backhaul link is performed between the BS andthe relay and communication in an access link is performed between therelay and the UE. Accordingly, the BS or the UE shown in FIG. 13 may bereplaced with the relay according to situation.

Referring to FIG. 22, a wireless communication system includes a BS 110and a UE 120. The BS 110 includes a processor 112, a memory 114, and aRadio Frequency (RF) unit 116. The processor 112 may be configured toperform the proposed procedures and/or methods according to the presentinvention. The memory 114 is connected to the processor 112 and storesvarious types of information related to operations of the processor 112.The RF unit 116 is connected to the processor 112 and transmits and/orreceives radio signals. The UE 120 includes a processor 122, a memory124, and an RF unit 126. The processor 122 may be configured to performthe proposed procedures and/or methods according to the presentinvention. The memory 124 is connected to the processor 122 and storesvarious types of information related to operations of the processor 122.The RF unit 126 is connected to the processor 122 and transmits and/orreceives radio signals. The BS 110 and/or the UE 120 may include asingle antenna or multiple antennas.

The embodiments of the present invention described above arecombinations of elements and features of the present invention in apredetermined form. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present invention may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present invention may be rearranged. Someconstructions of any one embodiment may be included in anotherembodiment and may be replaced with corresponding constructions ofanother embodiment. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentinvention or included as a new claim by subsequent amendment after theapplication is filed.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, the methods according to exemplaryembodiments of the present invention may be achieved by one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, an embodiment of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. Software code may be stored in a memory unit and executedby a processor. The memory unit may be located at the interior orexterior of the processor and may transmit and receive data to and fromthe processor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method of transmitting and receiving an SS forD2D communication in a wireless communication system and the apparatustherefor have been described centering on an example applied to a 3GPPLTE system, the present invention is applicable to a variety of wirelesscommunication systems in addition to the 3GPP LTE system.

1. A method of transmitting a signal for device-to-device (D2D)communication by a user equipment (UE) in a wireless communicationsystem, the method comprising: transmitting a synchronization signal forD2D communication and a demodulation reference signal (DM-RS) fordemodulating the synchronization signal, wherein a base sequence of theDM-RS is generated using a synchronization reference identity (ID). 2.The method according to claim 1, wherein the base sequence is generatedbased on a value obtained by dividing the synchronization reference IDby a predetermined value.
 3. The method according to claim 1, wherein anorthogonal cover code (OCC) for the DM-RS is determined using one lowerbit of the synchronization reference ID.
 4. The method according toclaim 1, wherein a cyclic shift for the DM-RS is determined using threelower bits of the synchronization reference ID.
 5. A user equipment (UE)for transmitting a signal for device-to-device (D2D) communication in awireless communication system, the UE comprising: a radio frequency (RF)unit; and a processor, wherein the processor is configured to transmit asynchronization signal for D2D communication and a demodulationreference signal (DM-RS) for demodulating the synchronization signal,and wherein a base sequence of the DM-RS is generated using asynchronization reference identity (ID).
 6. The UE according to claim 5,wherein the base sequence is generated based on a value obtained bydividing the synchronization reference ID by a predetermined value. 7.The UE according to claim 5, wherein an orthogonal cover code (OCC) forthe DM-RS is determined using one lower bit of the synchronizationreference ID.
 8. The UE according to claim 5, wherein a cyclic shift forthe DM-RS is determined using three lower bits of the synchronizationreference ID.